Radio antennas

ABSTRACT

An antenna for a wide bandwidth electromagnetic field polarized in a predetermined direction at right angles to the field propagation direction includes plural metal elements that are not resonant in the bandwidth. The metal elements are excited to transduce an electric field in the polarization direction over the bandwidth range. The plural elements have an extent in the polarization direction no greater than an order of magnitude of the shortest wave length in the bandwidth. A structure between the element, which may be either a coil or parallel electrodes which derive a displacement current, transduces a magnetic field having lines of flux at right angles to the polarization and propagation directions. The electric and magnetic fields are excited by power from the same source with phases so that in an interaction region of the field between a pair of the metal elements there is E×H synchronism and a radiation Poynting vector having rotational E and H fields to transduce the electromagnetic field.

FIELD OF THE INVENTION

This invention relates to antennas for the transmission and reception ofradio waves for telecommunications, broadcasting sound and television,radar, satellite communications and the like.

Known antennas usually have a single feeder connected to either a singleconductor element of approximately half a wavelength, or to a singledriven element within a group of parasitic elements as in the Yagi-Udaarray. By means of added reactive components such as inductors, endcapacitors, resonant traps and such, antennas have been constructed withsomewhat smaller dimensions than the basic half wavelength element. Loopantennas are also known and are useful in direction finding. Howevermost antennas of reduced dimensions have disappointing transmissionefficiency due to the necessarily increased circulation currents whichcause large conductor losses and or magnetic core losses.

BACKGROUND ART

The Poynting Theorem states that for any superimposed electric andmagnetic fields there must be energy flowing in the medium and thus thephenomenon of radio wave propagation has been explained in the presentlyaccepted theory as the radiation of electromagnetic energy in the formof an electric field E and a magnetic field H in a cross-productPoynting vector E×H=S watts per meter squared. The perpendiculargeometric relationship and the time synchronism implied by the aboveformula must be produced by any antenna which is to radiate efficiently.Presently known antennas are probably achieving the requirements in anuncontrolled or accidental manner.

Due to extended physical dimensions and high location above the ground,it is probable that there is fortuitously provided in the large volumeof space a means of setting the necessary perpendicularity andsimultaneity as well as a degree of rotationality for the fields,although the absence of these conjectures from the present texts oughtnot to be used to condemn the validity of the concept. From the largesurrounding and lightly stressed volume the comparatively weak Poyntingvector progresses outwards to infinity.

THE INVENTION

In accordance with one aspect of the invention a radio antenna in whichelectromagnetic waves are radiated from a small volume comprises twofirst and second separate element systems respectively excited forproducing high frequency electric and magnetic fields. Separate feedermeans drives each of the element systems. Each of the element systems ispositioned in adjacent interactive relationship to cross stress a commoninteraction zone of both fields to create a source from whichelectromagnetic waves radiate. The element system in which the electricfield is originated establishes a radio frequency potential differenceacross an interaction zone between two conducting surfaces. The elementsystem for establishing the magnetic field includes two other conductingsurfaces for establishing an intense radio frequency displacementcurrent. A radio frequency potential difference of the same frequency isapplied between two of the conducting surfaces for establishing anintense circulating magnetic field to cross the interaction zone.

In a preferred embodiment a phasing unit splits an output of a radiotransmitter into two parts having separate delay arrangements to producesynchronized electric and magnetic fields at the interaction zone. Thephasing unit preferably includes fixed and variable phase delay circuitsand at least one tapped transformer and a switch for adjusting each partof the output of the radio transmitter. The phasing unit also preferablyhas a wideband constant phase different circuit for low power operationfor driving either of the separate units. Two separate power amplifiersdevelop sufficient power to provide separate feeds to the two separateelement systems of the antenna so that within the interaction zone radiowave power is synthesized.

In another embodiment a single feeder is connected to one element systemand a second feeder drives the other element system with a phase andmagnitude to synthesize a radio frequency wave at a predeterminedfrequency band.

In another embodiment, the two separate element systems are constructedas half structures with a conducting surface of sufficient area that theother half structure is defined by a virtual image thereof.

In accordance with a further aspect of the invention, an antennacomprises a first set of at least two spaced elements defining surfacelying an end to end relationship with each other. Radio frequency poweris fed to the set of elements for producing an E-field between the setof elements. A second set of at least two spaced elements definessurfaces in face to face parallel planes. Radio frequency power producesa displacement current between the second set of spaced elementsestablishes an H field around the second set. The first and secondspaced elements and means for feeding the radio frequency power arearranged so there is interactive coupling between the E and H fields toproduce a propagating electromagnetic radio wave.

In accordance with one embodiment the surfaces of the second set ofelements are positioned between the surfaces of said first set ofelements and perpendicular thereto. In one arrangement, the first set ofelements comprises parallel circular plates. In another arrangement thefirst set of elements comprises plates and the second set of elementscomprises parallel plates.

In one embodiment one of the fields is produced by a feed including acoaxial feeder cable coupled through a transformer including a ferritetoroidal core. The first and second sets of elements are preferablysecured and spaced by electrically insulating support members. Aground-plane structure may be provided wherein one of each of the spacedset of elements is constituted by a virtual image of the other elementon the other side of a ground plane element electrically bisecting theantenna.

In accordance with a further aspect of the invention, an antenna forwide bandwidth electromagnetic field polarized in a predeterminedposition at right angles to the field propagation direction comprisesplural metal first elements that are not resonant in the bandwidth. Thefirst elements are excited to transduce an electric field in thepolarization direction over the bandwidth and have an extent in thepolarization direction no greater than an order of magnitude less thanthe shortest wavelength in the wide bandwidth range. Means between theelements transduces a magnetic field having lines of flux between theelements at right angles to the polarization and propagation directions.The elements and means are arranged and the electric and magnetic fieldsare excited by power from the same source with phases so there is aninteraction region of the fields between a pair of the metal elements toprovide E×H synchronism and a radiation Poynting vector havingrotational E and H fields to transduce the electromagnetic field. Theelements include first and second metal plates having spaced planarfaces substantially at right angles to the electric field. The platesare excited with voltages displaced in phase by 180° so the electricfield is established between said planar faces. A coil disposed betweenthe plates has windings positioned to excite the lines of flux. The coilis excited with current from the same source which excites the plateswith a current displaced in phase by 90° relative to the voltages whichexcite the plates.

In one embodiment, the faces of the plates diverge from a central regionwhere the coil is located so curved electric field lines extend betweenthe plates.

In another embodiment, the elements include first, second, third andfourth metal plates having spaced planar faces substantially at rightangles to the electric field. The first and second plates are excitedwith a first voltage having the same phase while the third and fourthplates are excited with a second voltage having the same phase. Thefirst and second voltages are from the same source and displaced inphase from each other by 180°. A coil disposed between the plates haswindings positioned to excite the lines of flux. The coil is excitedwith current from the same source which excites the plates with acurrent displaced in phase by 90° relative to the voltages which excitethe plates. Preferably, the faces of the plates diverge from a centralregion where the coil is located so curved electric field lines extendbetween the first and third plates and between the second and fourthplates.

In a further embodiment, at least one of the metal elements has a firstsurface extending (a) in substantially the same direction as theelectric field, (b) at substantially right angles to the magnetic linesof flux and (c) at substantially right angles to the propagationdirection so the electric field is curved as it propagates from thefirst surface to a second surface of another of the metal elements. Theelements including the first and second surfaces are excited withvoltages from the same source that are displaced 180° from each other.Preferably, the another element including the second surface isconfigured so the first and second surfaces extend in substantially thesame direction. In one embodiment the first and second surfaces aresubstantially planar and substantially aligned. In a second embodimentthe first and second surfaces are cylindrical and have substantially thesame radii and substantially common axes. The another second element maybe a planar surface extending in a plane substantially parallel to thepropagation direction. In this case, the first surface is cylindricaland the first surface has an axis substantially at right angles to theplane of the second element. In the further embodiment, the magneticfield is transduced by a coil disposed between the elements and havingwindings positioned to excite the lines of flux. The coil is excitedwith current from the same source which excites the elements with acurrent displaced in phase by 90° relative to the voltages which excitethe elements. In this arrangement the another element is configurated sothe first and second surfaces extend in substantially the same directionand the first and second surfaces are preferably substantially planarand substantially aligned.

In still another embodiment the magnetic field is transduced by acapacitor having first and second substantially parallel planarelectrodes extending substantially in the direction of propagation andsubstantially at right angles to the electric field lines. Theelectrodes are excited so voltages phase displaced from each other by180° are applied to the first and second electrodes so a displacementcurrent correlated with the magnetic field subsists. In thisarrangement, preferably at least one of the metal elements has a firstsurface extending (a) in substantially the same direction as theelectric field, (b) substantially at right angles to the magnetic linesof flux and (c) substantially at right angles to the propagationdirection so the electric field is curved as it propagates from thefirst surface to a second surface of another of the metal elements. Theelements are excited by a means including the first and second surfaceswith voltages from the same source that are displaced 180° from eachother. The another element is preferably configured so the first andsecond surfaces extend in substantially the same direction and the firstand second surfaces are substantially planar and substantially aligned.

The first and second surfaces are cylindrical in still anotherarrangement wherein the first and second surfaces have substantially thesame radii and substantially common axes. The second element may includea planar surface that extends in a plane substantially parallel to thepropagation direction, in which case the second element preferablyincludes the second electrode. A first cable includes a first feed lineextending through a central aperture of the first electrode. The firstline is connected to the first element and a second line connected tothe second element. A second cable including third and fourth lines isconnected to terminals of a primary winding of a transformer having asecondary winding having opposite terminals respectively connected tothe first electrode and the second element. The cables may be coaxial sothe first and third lines are respectively center conductors of thefirst and second cables and the second and fourth lines are respectivelyshields of the first and second cables.

The invention is further described and illustrated with reference to theaccompanying drawings, showing embodiment by way of examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of an embodiment with a horizontal coil,

FIG. 2 is a schematic elevation view of the embodiment of FIG. 1,

FIG. 3 is a circuit diagram for phasing unit for feeding an antennaaccording to the invention,

FIG. 4 is a circuit diagram of a further feeder unit,

FIG. 5 is a schematic perspective view of another embodiment forradiating of vertically polarized waves,

FIG. 6 is a schematic perspective view of a further embodiment usingcapacitive effect to produce the magnetic field,

FIG. 7 is a schematic perspective view of an embodiment similar to FIG.6 using cylindrical elements.

FIG. 8 is a schematic perspective view of an embodiment forming a groundplane construction, and

FIG. 9 is a schematic perspective view of the feed arrangement for anantenna similar to that shown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a plan view of an elementary form of a twin feeder crossedfield antenna according to this invention. The horizontal coil 1 is fedby feeder 2 via matching and isolating transformer 3 and carries a radiofrequency current shown by arrows indicating an anticlockwise maximum inthe cycle time. Thus upwardly directed in the center of the coil thereis high magnetic field density H from J+D'=∇XH which returns downwardsall around the periphery of the coil. There are two pairs of conductingplates 4 and 5, 6 and 7, with planes standing vertically which areinsulated from everything else but are fed with antiphase voltage of thesame frequency in pairs as shown, by power in feeder 8 via matching andisolating transformer 9. At the same instant in the cycle the plate pair4 and 5 are electrically positive relative to the plate pair 6 and 7.Thus due to the very small dimension of the whole antenna, thepropagation delay across the interaction zones marked X and Y isnegligible and so the correct simultaneity, orthogonality androtationality exists and Poynting vector synthesis occurs and radiopower radiates away with the velocity of light in the directions markedS.

FIG. 2 is a diagram of the same antenna in elevation.

Detailed consideration of the phase requirement may be deduced asfollows. Sinusoidal carrier waves are being applied and electric field Eis in phase with the voltage across the plate pairs. The retardation dueto size is negligible as is the magnetic field retardation around thecoil. Thus the field H is in synchronism with the current causing it,that is the magnetic field is in phase with the current. Current in acoil is however always lagging by about 90° relative to the voltageacross the coil due to self inductance. So, in order to obtain phasesynchronism of the fields interacting in the crossed field antenna, thefeed voltage to the coil needs to be approximately 90° advanced on thefeed voltage between the electrical plates. If both transformers haveidentical phase characteristics, the signal to feeder 2 must to be phaseadvanced by 90° compared with the voltage supplied to feeder 8. Cablelengths are only significant if different, so for a single frequencyapplication an electrical quarter wavelength extra in feeder 8 wouldfulfil the phase requirement. By providing a power divider so that asingle transmitter supplies approximately half the power to each of thetwin feeders, the interaction zone radiates the total power in thesynthesised Poynting vector An antenna for general radio communicationsrequiring many operational frequency changes must to have a phaseadjusting unit.

FIG. 3 is a circuit diagram of a simple phasing unit with which the saidphase adjustment could be provided The transmitter power is split partlyinto the upper capacitive path and partly into the lower inductive path.Setting the capacitor 10 to some value will give 45° advance; settingthe inductor to another value will result in a corresponding 45° delaywhich will ensure that after stimulating the two fields the radio wavewill be correctly synthesised in the interaction zones.

FIG. 4 shows a more sophisticated form of phasing unit which willprovide phasing for any kind of twin feeder crossed field antenna underalmost any circumstances over a wide frequency range. A switched autotransformer 12 is connected to feeder output 88 and is preceded by phaseadjustment arrangements switchable into either sense by switch 14, ofwhich coarse settings are provided by the dual gang switch 13A, 13B anda selection of cable lengths 15, and a fine adjustment by the variablecapacitor 16.

A more complex phase adjustment system, (not shown) would have a seriesof two-pole change-over switches able to connect any total combinationof delay cables selected from a sequence of lengths incremented in a1/8, 1/4, 1/2, 1, 2, 4, 8, 16, 32 metersystem. Such a scheme would allowa user to correct the phase of the feed to a crossed field antenna suchthat a single device could be radiating successfully at any frequency inthe whole HF spectrum.

In a further preferred arrangement the phasing unit has a widebandconstant phase difference circuit for low power operation and followed,either inside the unit or outside as two separate units, by two separatepower amplifiers which develop sufficient power to provide separatefeeds to the two electrode systems of the antenna so that within theinteraction zone sufficient radio wave power is synthesised.

An alternative twin feeder crossed field antenna which will radiatevertically polarized waves instead of horizontal, is shown in FIG. 5.The antenna consists of a narrow vertical coil 17 fed from cable 2C viamatching transformer 18, and two conducting plates 19 and 20 fed byfeeder 8C via matching and isolating transformer 21. A widespreadelectric field E is created in arcs from the top plate to the lowerplate and produces a cross-product with the magnetic field H rotating inthe directions indicated and thus synthesises intense Poynting vectors Swhich radiate outwards in broad azimuthal angles to space. The saidantenna having several advantageous features namely a reduced number ofcomponents and also a larger interaction volume than has the first typeaccording to FIGS. 1 and 2. The first feature reduces costs andsimplifies the structure. The second advantage gives enhanced signalvoltages when used in the receive mode. Furthermore, since any one ofthe four input terminals (two plates and two coil terminals) may beconnected to earth it will be optimal to have the lower plate earthedfor safety as well as providing an opportunity to bond the screens ofthe coaxial feeders thereto.

It is possible for transformer 21 to be dispensed with, and direct feedfrom the inner conductor of feeder 8C to be connected to the upper plate19 with the screen remaining connected to plate 20.

As a further development of the twin feeder crossed field antenna typeswhich use a coil to generate the magnetic field, a further arrangementis proposed called the Maxwell type, in which the magnetic field isproduced from an electric field displacement current located within acapacitor. It is an arrangement which has many advantages theoreticallyand practically, and allows the construction of a truly omnidirectionalvertically polarised antenna. Examination of the Maxwell law D'=∇XHwhere D'=δD/δt shows that a changing displacement field causes arotational magnetic field. As the displacement current density is simplyrelated in space (or in air) by the formula D'=εE' where E is theelectric field intensity and ε is the dielectric constant, it is easy tocalculate that this will be a very useful technique for HF crossed fieldantennas of small size. Also it can be seen that as before, the S= E×Hrelationship of the Poynting vector demands geometric perpendicularitysynchronism and rotational form to both fields The differentiation withrespect to time within the Maxwell law again inserts a 90° phase changebut in this type it is of the opposite sign. There is a 90° advance ofmagnetic field relative to the voltage gradient and so there must be a90° delay in the voltage fed to the plates of the said capacitor. TheMaxwell type of crossed field antenna requires two separate electricfield stimulator plates; one pair as in the first type to initiate the Efield, and the other pair to initiate the magnetic field by the Maxwelllaw The second pair are called therefore, the D plates. In total thereare four phases of electric potential within the antenna structure: 0°and 180° of the E plates; 90° and 270° of the D plates

FIG. 6 is a diagram of a basic form of the Maxwell type of twin feedercrossed field antenna. Two flat plates 22 and 23, standing verticallyare insulated from other electrodes and ground and are fed by coaxialcable 26 via matching and isolating transformer 27, thereby producingthe electric field E shown in the downwards phase. Two insulated flatelliptical plates 24 and 25, disposed horizontally are also insulatedfrom earth and other electrodes and constitute the capacitor withinwhich a large displacement current density D' is produced by radiofrequency power arriving from feeder 28 via matching and isolatingtransformer 29. The rapidly changing displacement current is then theorigin of the considerably curved H around the whole antenna in thedirection shown. In the wide interaction zones at mid height, in frontof and behind the structure, copious field crossing is present and soconsiderable Poynting vector power density is generated and radio wavespropagate away at the velocity of light in the directions shown S. Thewaves are vertically polarised; the horizontal polar diagram is a figureof eight. The lower plate may be earthed and the screens of the coaxialfeeders bonded to it. The transformer 27 may be dispensed with and adirect connection made between the inner of the feeder 26 and the plate23.

Many variants of the Maxwell type are conceivable and they constitute ageneric family of twin feeder crossed field antennas disclosed herein.For instance the form described in FIG. 6 could be turned through 90°and it will then generate horizontally polarised waves and have aradiation polar diagram which is a figure of eight in the horizontalplane.

Two further antennas of this family will b described as they areimportant in having a robust structural shape as well as a verticallypolarised omnidirectional radiation which is often required inbroadcasting and communicating to mobiles

FIG. 7 is a diagram of the cylindrical form of Maxwell type crossedfield antenna. The downwards electric field E is initiated by voltagebetween the hollow cylindrical conducting electrodes 30 and 31 which arefed from feeder via matching transformer 33 The lower cylinder may standsafely on the ground or could be formed as a flat plate on site. Thedisplacement current D' is stimulated upwards at the same time in thecycle by feeding the appropriate phase voltage between the twohorizontal disc conductors 34 and 35 (having their central area removedfor space to mount transformers, feeders etc.) using feeder 36 viamatching and isolating transformer 37. Should there be a requirement toreduce weight or wind resistance, the said electrodes and conductors maybe made with alternative materials such as conducting wire mesh, or aconducting surface applied to a plastics or other non-conductingstructural component.

FIG. 8 is a diagram of a ground plane (or half symmetry) form of thecylindrical twin feeder crossed field antenna of the Maxwell type. Thedownwards electric field E is produced by applying a voltage between thehollow conducting cylinder 37 and the large conducting earth plane 38with the upwards displacement current D' from the said earth plane tothe circular conducting plate 39 with a central missing area marked 39ain order to create the required rotational magnetic field H to interactwith the said E field and synthesise the Poynting vector S radiating allround to space.

In a practical construction for the frequency range 3.6 to 30 MHz, thecylinder 37 has a height of 25 cm and a diameter of 20 cm with the basespaced 10 cm from the plate 39. Plate 39 has a diameter of 40 cm and ispositioned coplanar to and 5 cm distance from plane 38. The parts may bemechanically connected by insulating pillars or foamed plastics blocks.

The feed arrangement is shown in FIG. 9 and this has the E-field feeder90 connected between ground plane 38 and cylinder 37 and the H-fieldfeeder 91 terminating in toroidal ferrite coupling transformer 92feeding between ground plane 38 and plate 39. It is important that theouter conductor of feeder 91 is not electrically connected with any partof the structure.

For weatherproofing the structure may be encased for protection but in apreferred embodiment a louvred or apertured screen is used inconjunction with a top cover to provide air through flow.

Twin feeder crossed field antennas of the above forms or other forms maybe made almost as small as desired. With correct time phasing, the powerradiated from the interaction zones can be made as large as desired andis limited only by the necessary voltages at the electrodes and theultimate possibility of corona discharge. However since the plates arelarge in area compared with the surface areas for wire antennas theproblem is of comparative insignificance. Antennas of these types only1/200 th of a wavelength in length (and less in diameter) have been ableto radiate 400 watts on HF with no perceptible problems of electrodedistress Calculations show that for the magnitudes of voltage used inwire antennas, teraWatt capabilities will be possible with crossed fieldantennas. There are no large circulating currents in any conductor sincenothing is in resonance. It is a major advantage of the twin feedercrossed field antenna system that it is broadband, and low Q. For anygiven antenna radiating efficiently because it is correctly phased, thebandwidth is very broad, firstly because of the phase-sense of frequencychange acting by the Maxwell Law is the same sense as change due to awave on the delay cable, secondly because the two fields are bothoriginated from capacitor stimulus and also change in the same phasesense, thirdly the two fields interact in such a way as to provide alower input impedance in each capacitor and therefore self-optimise thesynthesis. Thus an antenna which is say 1/400 th of a wavelength heightmay be expected to have a small depreciation of efficiency by afrequency change of about plus and minus 15%.

Many of the electrical properties of the system described are notcritical. For instance the adjustments needed in the phasing unit toproduce a low VSWR in the common feeder leading will be found inpractice to be self-optimising. The magnetic field generated around thedisplacement current capacitor is in the direction of curvature toreduce the impedance experienced by the electric field generator sincethe synthesised Poynting vector takes away power from the radio wavecontinuously, and at no part of the cycle does the E field find its pathas impedant as normal space; it is always presented to the field linesas a power sink as long as the magnetic field H is synchronous For thesame reasons, the H field lines flow into a low reluctance interactionzone of a similar power sinking nature due to the cross-curved E fieldin phase at all times. Only in the unproductive zones around the antennado the fields experience the normal path impedance and reluctances. Thecrossed field antenna system is almost an efficient "open frequency"antenna It will also receive radio signals and so may be used in twoway-radio systems.

In fact the new device is such a small sized source that many techniquesnot before possible are now within easy achievement. When used in areflecting or phasing arrangement, the crossed field antenna allowsperceptible directivity to be attained in either transmit or receivemodes even when the waves concerned are much larger than the reflectoror array diameter.

The radio antenna may be used to radiate or receive electromagneticwaves when mounted within or along with other conductors, or conductingsurfaces in order to reflect, direct, focus or enhance the saidradiation or fed with either constant phase related power in parts, orvarying phase power in parts so that a shaped radiation pattern isproduced by the array and may be directed in any desired direction ordirections.

The invention also relates to the use of the antenna for radiocommunication through a medium comprising ground, water, air or space.

We claim:
 1. A radio antenna in which electromagnetic waves are radiatedfrom a small volume comprising two separate element systems, one of saidsystems being excited for producing a high frequency electric field, andthe other of said systems being excited for producing a high frequencymagnetic field, separate feeder means driving each of said elementssystems, each of said element systems being positioned in adjacentinteractive relationship to cross stress a common interaction zone ofboth said fields to create a source from which electromagnetic wavesradiate, the element system in which said electric field is originatedincluding means for establishing a radio frequency potential differenceacross an interaction zone between two conducting surfaces and in whichthe element system for establishing the magnetic field includes twoother second conducting surfaces for establishing an intense radiofrequency displacement current, and means for applying a radio frequencypotential difference of said same frequency between the said secondsurfaces for establishing an intense circulating magnetic field andcausing a significant portion of the circulating magnetic field to crosssaid interaction zone.
 2. A radio antenna according to claim 1 furtherincluding a phasing unit for splitting an output of a radio transmitterinto two parts having separate delay arrangements to producesynchronized electric and magnetic fields at the interaction zone.
 3. Aradio antenna according to claim 2, wherein the phasing unit includesfixed and variable phase delay circuits and at least one tappedtransformer and switch for adjusting each said part of the output of thesaid radio transmitter.
 4. A radio antenna according to claim 3, whereinthe phasing unit has a wideband constant phase difference circuit forlow power operation and for driving two separate power amplifiers fordeveloping power to provide separate feeds to the two separate elementsystem of the antenna so that within the interaction zone sufficientradio wave power is synthesized.
 5. A radio antenna according to claim 1further including a single feeder connected to one element system and asecond feeder for driving the other element system with a phase andmagnitude to synthesize a radio frequency wave at a predeterminedfrequency band.
 6. A radio antenna according to claim 1 wherein the twoseparate element systems are constructed as half structures with aconducting surface of sufficient area that the other half structure isdefined by a virtual image thereof.
 7. A antenna comprising a first setof at least two spaced elements defining surfaces lying in end to endrelationship with each other, means for feeding radio frequency power tothe set of elements for producing an E-field between the set ofelements, a second set of at lest two spaced elements defining surfacesin face to face parallel planes, means for feeding radio frequency powerto produce a displacement current between the second set of spacedelements for producing an H field around the second set, the first andsecond spaced elements and the means for feeding being arranged suchthat there is interactive coupling between said E-field and said H-fieldto produce a propagating electromagnetic radio wave.
 8. An antennaaccording to claim 7, wherein the surfaces of said second set ofelements are positioned between the surfaces of said first set ofelements and perpendicular thereto.
 9. An antenna according to claim 8,wherein the first set of elements comprise coaxial cylinders, the secondset of elements comprising parallel circular plates.
 10. An antennaaccording to claim 8, wherein the first set of elements comprise plates,the second set of elements comprising parallel plates.
 11. An antennaaccording to claim 7 wherein the means for feeding radio frequency powerto the elements for producing at least one of the fields comprises acoaxial feeder cable coupled through a transformer including a ferritetoroidal core.
 12. An antenna according to claim 7 wherein said firstand second sets of elements are secured and spaced by electricallyinsulating support members.
 13. An antenna according to claim 7 furtherincluding a ground-plane structure wherein one of each of the spaced setof elements is constituted by a virtual image of the other said elementon the other side of a ground plane element electrically bisecting theantenna.
 14. An antenna for an electromagnetic field polarized in apredetermined direction at right angles to the field propagationdirection, the field having a wide bandwidth range, the antennacomprising plural metal first elements that are not resonant in saidbandwidth range excited to transduce an electric field in saidpolarization direction over said bandwidth range, said plural elementshaving an extent in the polarization direction no greater than an orderof magnitude less than the shortest wavelength in the wide bandwidthrange, means between said elements excited for transducing a magneticfield having lines of flux between said elements at right angles to thepolarization and propagation directions, said elements and means beingarranged and said electric and magnetic fields being excited by powerfrom the same source with phases so that there is an interaction regionof said fields between a pair of said metal elements to provide E×Hsynchronism and a radiation Poynting vector having rotational E and Hfields to transduce said electromagnetic field, said elements includingfirst and second metal plates having spaced planar faces substantiallyat right angles to the electric field, means for exciting the plateswith voltages displaced in phase by 180° so the electric field isestablished between said planar faces, a coil disposed between saidplates and having windings positioned to excite said lines of flux, andmeans for exciting said coil with current from the same source whichexcites the plates with a current displaced in phase by 90° relative tothe voltages which excite the plates.
 15. The antenna of claim 14wherein the faces of the plates diverge from a central region where thecoil is located so that curved electric field lines extend between theplates.
 16. The antenna of claim 14 wherein said elements include first,second, third and fourth metal plates having spaced planar facessubstantially at right angles to the electric field, means for excitingthe first and second plates with a first voltage having the same phaseand for exciting the third and fourth plates with a second voltagehaving the same phase, the first and second voltages being from the samesource and displaced in phase from each other by 180°, a coil disposedbetween said plates and having windings positioned to excite said linesof flux, and means for exciting said coil with current from the samesource which excites the plates with a current from the same sourcewhich excites the plates with a current displaced in phase by 90°relative to the voltages which excite the plates.
 17. The antenna ofclaim 16 wherein the faces of the plates diverge from a central regionwhere the coil is located so that curved electric lines extend betweenthe first and third plates and between the second and fourth plates. 18.The antenna of claim 14 wherein at least one of the metal elements has afirst surface extending (a) in substantially the same direction as theelectric field, (b) at substantially right angles to the magnetic linesof flux and (c) at substantially right angles to the propagationdirection so that the electric field is curved as it propagates fromsaid first surface to a second surface of another of the metal elements,and means for exciting the elements including said first and secondsurfaces with voltages from the same source that are displaced 180° fromeach other.
 19. The antenna of claim 18 wherein said another elementincluding the second surface is configured to that the first and secondsurfaces extend in substantially the same direction.
 20. The antenna ofclaim 19 wherein the first and second surfaces are substantially planarand substantially aligned.
 21. The antenna of claim 19 wherein the firstand second surfaces are cylindrical, the cylindrical surfaces havingsubstantially the same radii and substantially common axes.
 22. Theantenna of claim 18 wherein said another element has a planar surfacethat extends in a plane substantially parallel to the propagationdirection.
 23. The antenna of claim 22 wherein the first surface iscylindrical, the first surface having an axis substantially at rightangles to the plane of the second element.
 24. The antenna of claim 18wherein the means to transduce the magnetic field includes a coildisposed between said elements and having windings positioned to excitesaid lines of flux, and means for exciting said coil with current fromthe same source which excites the elements with a current displaced inphase by 90° relative to the voltages which excite the elements.
 25. Theantenna of claim 24 wherein said another element is configured so thatthe first and second surfaces extend in substantially the samedirection.
 26. The antenna of claim 25 wherein the first and secondsurfaces are substantially planar and substantially aligned.
 27. Theantenna of claim 14 wherein the means to transducer the magnetic fieldcomprises a capacitor having first and second substantially parallelplanar electrodes extending substantially in the direction ofpropagation and substantially at right angles to the electric fieldlines, and means for exciting the electrodes so that voltages phasedisplaced from each other by 180° are applied to the first and secondelectrodes so that a displacement current correlated with the magneticfield subsists between the electrodes.
 28. The antenna of claim 27wherein at least one of the metal elements has a first surface extending(a) in substantially the same direction as the electric field, (b)substantially at right angles to the magnetic lines of flux and (c)substantially at right angles to the propagation direction so that theelectric field is curved as it propagates from said first surface to asecond surface of another of the metal elements, and means for excitingthe elements including said first and second surfaces with voltages fromthe same source that are displaced 180° from each other.
 29. The antennaof claim 28 wherein said another element in configured so that the firstand second surfaces extend in substantially the same direction.
 30. Theantenna of claim 29 wherein the first and second surfaces aresubstantially planar and substantially aligned.
 31. The antenna of claim28 wherein the first and second surfaces are cylindrical, the first andsecond surfaces having substantially the same radii and substantiallycommon axes.
 32. The antenna of claim 28 wherein the second element hasa planar surface that extends in a plane substantially parallel to thepropagation direction.
 33. The antenna of claim 32 wherein the secondelement includes the second electrode.
 34. The antenna of claim 33wherein the first electrode includes a central aperture, a first cableincluding a first feed line extending through the aperture and connectedto said first element and a second line connected to said secondelement, a second cable including third and fourth lines connected toterminals of a primary winding having opposite terminals respectivelyconnected to the first electrode and the second element.
 35. The antennaof claim 34 wherein said cables are coaxial, the first and third linesbeing center conductors of the first and second cables, respectively,the second and fourth lines being shields of the first and secondcables, respectively.
 36. The antenna of claim 33 wherein the firstsurface is cylindrical, the cylindrical surface having an axis at rightangles to the plane of the second element.